Extensive Poison Hemlock in Backyard - Ask Extension
I recently discovered that my yard is full of poison hemlock in the year 2 growth stage (tons of tall, flowering stalks). A company is proposing to co...
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Extensive Poison Hemlock in Backyard #874013
Asked June 20, 2024, 9:50 PM EDT
I recently discovered that my yard is full of poison hemlock in the year 2 growth stage (tons of tall, flowering stalks). A company is proposing to come cut it all down to the ground and remove it, spray with herbicide, and spread pre-emergent herbicide granules. Is this an effective plan? My next door neighbor's yard is full of this same plant in the flowering stage as well and I'm not sure if they are going to remove it so I'm expecting plenty of those seeds to end up in my yard.
What steps do you recommend I take in the months/years ahead to prevent recurrence after this initial outbreak is removed? Thank you!
Multnomah County Oregon
Expert Response
Autumn: Poison hemlock is what we call a biennial plant. The ones that are tall now started last spring/summer and overwinter as a "rosette", which is visible all winter. The second thing to know is that it takes bare ground to grow, It doesn't grow in lawns or other spaces with competitive plants. Spraying the tall plants now may not stop them from dropping more seeds. It is better to cut and remove them quickly so you don't add to the seeds in the soil. You need to know that the plants and sap are toxic to your skin, eyes, etc. so do this with care or have someone else that knows what they are doing, remove them.
There are some herbicides that are effective on poison hemlock but, as noted above, are most effective on younger plants. You didn't describe the area that they were growing in. There may be some options to grow grass or other plants that make it difficult for the seeds to germinate. Let me know a little more about the situation where they are growing. A picture would help.
Chip Bubl OSU Extension Agent (retired) Columbia County <personal data hidden><personal data hidden>
There are some herbicides that are effective on poison hemlock but, as noted above, are most effective on younger plants. You didn't describe the area that they were growing in. There may be some options to grow grass or other plants that make it difficult for the seeds to germinate. Let me know a little more about the situation where they are growing. A picture would help.
Chip Bubl OSU Extension Agent (retired) Columbia County <personal data hidden><personal data hidden>
